login

Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.

Primes p such that the greatest common divisor of 2^p+1 and 3^p+1 is composite.
2

%I #24 Dec 06 2021 03:13:20

%S 2243399,2334547,2743723,3932207,4623107,4716343,5482423,5993411,

%T 6490151,7156769,7187743,8795167,9026987,9608843,9923209

%N Primes p such that the greatest common divisor of 2^p+1 and 3^p+1 is composite.

%H Carlos Rivera, <a href="https://www.primepuzzles.net/puzzles/puzz_1064.htm">Puzzle 1064. GCD(2^p+1,3^p+1)</a>, The Prime Puzzles and Problems Connection.

%o (PARI) isok(p) = if (isprime(p), my(g=gcd(2^p+1, 3^p+1)); (g>1) && !isprime(g));

%Y Subsequence of A260674.

%Y Cf. A066803.

%K nonn,more

%O 1,1

%A _Michel Marcus_, Nov 27 2021

%E a(4)-a(7) after update of Rivera link from _Martin Ehrenstein_, Dec 04 2021

%E a(8)-a(9) from _Shyam Sunder Gupta_, Dec 04 2021

%E a(10)-a(15) from _Martin Ehrenstein_, Dec 05 2021